1. Field of the Invention
This invention relates to rotating machinery, and is particularly directed to vaneless, multistage, centrifugal pumps and the like having a radial diffuser and a spiral crossover between stages.
2. Description of Prior Art
In centrifugal pumps, it is customary to provide a diffuser portion which receives fluid flow exiting the impeller and serves to convert the flow velocity, imparted by impeller, into increased pressure by allowing the flow cross section to increase. In multistage pumps, it is necessay to divert the direction of fluid flow in the diffuser in order to guide the flow to the impeller inlet of the next stage. Where pure fluids are being transported, these directional changes can be quite abrupt and vanes can be provided to assist in diverting the flow direction. However, when highly abrasive materials, such as coal slurry, are being transported, the flow direction must be changed very gradually in order to avoid destructive erosion of the pump housing. Also, flow directing vanes become eroded so rapidly that they are of questionable value. In order to avoid these problems in transporting highly abrasive materials, it has been customary to employ conduits external to the pump housing for changing the flow direction from the output of one stage to the inlet of the next. Such conduits are substantially cheaper and easier to replace than the pump housing and, hence, have served to reduce the cost of such pumps and the "down time" involved in making repairs. On the other hand, such external conduits are less efficient and are extremely bulky, especially where the slurry is to be transported at high pressures, and are susceptable to damage from external sources.